1. Field of the Invention
The present invention relates to a brushless DC motor, and more particularly to a brushless DC motor in which electronic components necessary for rotary drive are built-in and at the same time which has a reduced dimension in the axial direction.
2. Description of the Related Art
Motor structures, in which electronic components are provided as constituent parts of a motor in a unified manner, are conventionally known. For example, Japanese Patent Application Laid-Open No. 2002-291194 discloses a brushless DC motor which includes electro components arranged around the outer circumference of a rotor assembly. Also, Japanese Patent Application Laid-Open No. 2007-60844 teaches a motor structure which is configured such that electronic components are located to overlap with a rotor magnet with respect to the axial direction so as to sandwich a motor case. Further, Japanese Patent Application Laid-Open No. 2005-57855 describes a brushless DC motor which is structured such that openings are provided at an upper housing of the brushless DC motor, wherein a hall element which is fixedly mounted on a circuit board is adapted to oppose the upper face of a rotor assembly through the openings.
The conventional motor structures described above, however, have the following problems. In the motor described in Japanese Patent Application Laid-Open No. 2002-291194, in which electronic components are arranged around the outer circumference of a rotor assembly, the radial dimension of the motor cannot be reduced. On the other hand, the motor structure described in Japanese Patent Application Laid-Open No. 2007-60844, which is configured such that electronic components are located outside a motor case, has advantage in that the radial dimension can be kept small but is disadvantageous in that the axial dimension (motor height) has to be increased. In the meantime, Japanese Patent Application Laid-Open No. 2005-57855 does not refer to any motor structure in which electronic components are arranged as constituent parts inside a housing member and at the same time are prevented from interfering with a rotor assembly.